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HISTORY OF TECHNOLOGY, TECHNOLOGY, OBJECTS AROUND US
Holography. History of invention and production
Directory / The history of technology, technology, objects around us Holography is a set of technologies for accurately recording, reproducing and reshaping the wave fields of optical electromagnetic radiation, a special photographic method in which images of three-dimensional objects are recorded and then restored using a laser, which are extremely similar to real ones.
The first holograms were obtained in 1947 by the Hungarian physicist Dennis Gabor, who was then working in England. This name goes back to the words "holos" (whole, completely) and "gram" (writing). Before the invention of the Hungarian scientist, any photograph was flat. She conveyed only two dimensions of the subject. The depth of space eluded the lens. In search of a solution, Gabor started from one well-known fact. Rays of light thrown off by a three-dimensional object reach the film at different times. And they all make a different path for different times. In scientific terms: all waves come with a phase shift. The offset depends on the shape of the object. The scientist came to the conclusion that the volume of any object can be expressed in terms of the phase difference of the reflected light waves. “Of course, the human eye is not able to catch this delay of the waves,” Nikolai Malyutin writes in the journal World Pathfinder, “because it is expressed in very small time intervals. This value must be converted into something more tangible, for example, into brightness differences. This and succeeded by a scientist who resorted to one trick. He decided to superimpose a wave reflected from an object - that is, distorted - on a passing ("reference") wave. "Interference" occurred. Where the crests of two waves met, they amplified - a bright spot appeared there "If the crests of the wave were superimposed on the trough, the waves extinguished each other, a blackout was observed. So, with the mutual superposition of the waves, a characteristic interference pattern arises, an alternation of thin lines, white and black. This pattern can be captured on a photographic plate - a hologram. It will contain all information about the volume of the object caught in the lens. In order for the "volumetric portrait" to be very accurate and detailed, it is necessary to use light waves of the same phase and length. In daylight or artificial lighting, such a focus will not work. After all, light is usually a chaotic mixture of waves of different lengths. It has all colors: from short-wave blue radiation to long-wave red. These light components are out of phase in the most bizarre way." Since there were no sources of coherent light at that time, the scientist used the radiation of a mercury lamp, "cutting out" a very narrow spectral strip from it using various tricks. However, the power of the light flux at the same time became so meager that it took several hours to produce a hologram. The very quality of the holograms turned out to be very low. The reasons were in the imperfection of both the light source and the optical recording scheme itself. The fact is that when recording a hologram, two images appear at once on opposite sides of the plate. For the Hungarian scientist, one of them always turned out to be against the background of the other, and when photographing them, only one image turned out to be sharp, while the second created a blurry background in the picture. In this case, to see the image on the hologram, it must be illuminated through the radiation of the same wavelength that was used during recording. But there is also an obvious advantage: such a three-dimensional image is created by any, even the smallest, section of the hologram-plate, due to the fact that the beam scattered by each point of the object illuminates the hologram completely. It turns out that any of its points stores information about the entire illuminated surface of the object. The advent of the laser gave a new impetus to the development of holography, since its radiation has all the necessary qualities: it is coherent and monochromatic. In 1962 in the USA, physicists Emmett Leith and Juris Upatnieks created an optical scheme for a topographic installation, which is still used with some modifications. In order to eliminate image overlaps, the laser beam is split into two and directed to the plate at different angles. As a result, holographic images are formed by independent beams traveling in different directions.
Another fundamentally new method of holography was created by the Russian physicist Yuri Nikolayevich Denisyuk. The scientist used the interference of oncoming beams of light. Getting on the plate from different sides, the beams are added in the photoemulsion layer, forming a three-dimensional hologram.
With the advent of the laser, Gabor's long-standing idea was finally realized. In 1971, the scientist received the Nobel Prize in Physics for his invention. In 1969, Stephen Benton came up with a way to make holograms with ordinary, white light. “For this,” Malyutin notes, “with the help of a photomask - a thin layer with many micro-slots - it is necessary to make a “master hologram” and copy it in a holographic way. A slotted template, like prisms, splits daylight into the primary colors of the spectrum. Into each of the slots a light beam of a single wavelength comes in. This provides interference and helps to get a picture that is bright, multi-colored, sparkling with different colors depending on the angle of view - the same hologram that we have become accustomed to in recent years. " The main advantage of color holography lies in the fact that it can be copied by machine using a specific embossing technique. A colorful copy is exposed to a special light-sensitive layer - a photoresist varnish. This material has a high resolution. (It is used, for example, in microlithography to apply certain elements of a microcircuit to a board.) In our case, when mass replicating holograms, they first take a digital camera and photograph the object from all sides. The computer links the individual pictures. And now the XNUMXD image is ready. Then, in the laboratory, a laser "engraves" this picture on a photosensitive plate. It turns out a thin surface relief. By means of electrolysis, the "engraving" is applied to a nickel matrix. The matrix is needed for mass replication of holograms. Their prints - by the method of hot stamping - are obtained on metal foil. Now, as soon as a beam of light falls on the hologram, it begins to play with all the colors of the rainbow. Among this multicolor, the depicted object appears before the viewer. These holograms are cheap. You can make them in any quantity, as long as you have the equipment. Such holograms are used all over the world as stickers on product packaging and documents. They serve as an excellent protection against counterfeiting: it is very difficult to copy a holographic recording.
You can create holograms that depict objects that do not exist in reality. It is enough for the computer to set the shape of the object and the wavelength of the light falling on it. Based on these data, the computer draws a picture of the interference of the reflected rays. Passing a light beam through an artificial hologram, you can see a three-dimensional image of an invented object. According to Sergei Trankovsky: "Holography has become a real gift for engineers: now they can investigate and record processes and phenomena that are sometimes described only theoretically. For example, the blades of a turbojet aircraft engine heat up to hundreds of degrees during operation and deform. How the stress is distributed in this case in the part where its weak point is located, threatening destruction, it was either extremely difficult or even impossible to determine before. With the help of holographic methods, such studies are carried out without much difficulty. Illuminated by laser light, the hologram reconstructs the light wave reflected by the part when it was taken, and the image appears where the part used to be. If the detail remains in place, two waves appear at once: one comes directly from the object, the other - from the hologram. These waves are coherent and can interfere. In the event that the object undergoes deformation during the observation, its image is covered with stripes, which are used to judge the nature of the changes. Topographic control methods are very convenient. They make it possible to measure the amount of deformation of parts and the amplitude of their vibration, to study the surfaces of objects of complex shape, to monitor the accuracy of manufacturing both very large products (for example, mirrors several meters in diameter for telescopes) and miniature lenses (as in a microscope). An object can reflect light poorly, have an uneven surface, be completely transparent - this does not affect the quality of the hologram. Thanks to powerful laser pulses, holograms are recorded in thousandths of a second. Therefore, now it is possible to study explosions, electrical discharges and gas flows moving at supersonic speeds. With the help of a hologram, you can see through frosted glass or other obstruction that scatters light. A hologram is removed from the diffuser and one of the images restored from it is combined with the diffuser itself. Light waves traveling towards each other from the hologram and from the diffuser add up and cancel each other out. The barrier disappears, and the object behind it becomes visible in all its details. Modern technologists have a new idea. It is based on the ability of a laser to “make” a part of any shape and size from a workpiece according to a given program. It is enough to insert a hologram of a reference part inside a technological laser to get rid of the need to write a program and set up a laser installation. The hologram itself will "pick up" such a beam configuration and distribution of its intensity that the "cut out" part will be an exact copy of the standard. It is necessary to pay attention to another, very similar way of extracting useful signals, which is called optical filtering, or pattern recognition. In a similar way, you can search for the desired images among many other similar ones, such as fingerprints. To do this, it is necessary to make a hologram from the standard, and then put it in the path of the light beam reflected from the object under test. The hologram will let light through only from an object that is completely identical to the standard, "rejecting" other images. A bright spot at the output of the optical filter is a signal that an object has been detected. It is noteworthy that the search is carried out at a tremendous speed, unattainable using other methods, since it can be carried out automatically. "Holographic methods," Trankovsky writes, "are applicable not only to light - electromagnetic radiation, but also to any other waves. In particular, an object immersed in an opaque or turbid liquid can be seen with the help of sound. Acoustic vibration emitters create two coherent waves. One (subject) "sounds" the object, the second (reference) - the surface of the liquid. Their interference causes ripples on it - the so-called acoustic hologram. By illuminating it with a beam of laser light, they restore a three-dimensional image of an object lying in water. However, they do and in another way: the signal from a system of miniature microphones is recorded on a photographic plate in the form of blackening stripes, and then a three-dimensional image is restored from it with a laser beam. Author: Musskiy S.A.
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